Hi guys I have an escort mk6 1995 1.4l engine and have failed mot due to high co readings. HC and Lambda are good.Have taken it to a mechanic to try and fix it but havent found out what it could be for now.We have tested the maf and lambda which are good.Changed cat yesterday but still no pass on mot.He checked the spark plugs and he said he didnt see any sign of rich fuelling .The last thing i did to the car was replacing the fan switch because it stopped working. The normal one for my car operates at 103-98 and I have done one which operates at 92-88 does this effect the problem im having. Also what else could it be please .

common problem with these engines (cvh), valve stem oil seals go hard and start sucking through oil and playing havoc with readings

modified stem seals ( top hat design) very easy indeed to change ...

Dirty filthy oil is a no no too, always good to change the oil if possible before an mot too as dirty oil will raise the numbers....

Any blue puffs of smoke on start up ?

no blue puffs of smoke on start up

Well I would say a good quality oil and a new filter for sure, if you just do short journeys and the engine/engine oil cannot get up to operating temperature then the unburnt fuel vapour as well as other gases in the crankcase ventilation system will dilute the oil and will take ages to burn off,

This is an old trick on diesels a fresh oil change before an MOT due to all the nastys being recirculated by the EGR valve making the oil thick dirty and black. But this adheres to any vehicle really as all cars have one type of crank case ventilation system to some affect.

would the fan switch i changed cause the engine to still be running a bit cold since its kicking the fan in at 92 instead of 103 and cutting at 88 instead of 98

bump please